Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $36.35   13.579%   $41.286   $41.29   $41.30   $41.30  
  Purchase #2 $191.69   3.189%   $197.803   $197.80   $197.80   $197.80  
  Purchase #3 $88.76   11.320%   $98.8076   $98.81   $98.80   $98.80  
  Purchase #4 $192.64   13.783%   $219.1916   $219.19   $219.20   $219.20  
  Purchase #5 $245.26   4.866%   $257.1944   $257.19   $257.20   $257.20  
  Purchase #6 $43.29   6.505%   $46.106   $46.11   $46.10   $46.10  
  Purchase #7 $150.47   11.361%   $167.5649   $167.56   $167.55   $167.60  
  7 purchase totals = $948.46       $1,027.9535   $1,027.95   $1,027.95   $1,028.00